Insulating material for electric device coil and slot liner of rotating electric machine

ABSTRACT

The present invention improves the heat resistance and strength of insulation material inserted between a core and a coil of an electrical machine. A slot liner is placed between a core of an electric motor of an electric machine and a conductor of a coil. The slot liner has a multi-layer construction with an aggregate mica insulation sheet, which has excellent mechanical strength, and a peeled mica insulation sheet, which has excellent voltage resistance at high temperatures. The slot liner can include a main insulation sheet and a reinforcement sheet. The reinforcement sheet is placed between the main insulation sheet and the core at the ends of the slot.

BACKGROUND TO THE PRESENT INVENTION

The present invention relates to an insulation material used in coils of electrical machines. In particular, the present invention relates to the construction of a slot liner, which is placed inside slots in a core of an electrical machine and which insulates between the core and the coil conductor.

In order to ensure insulation between the coil and the core, the coil of the electrical machine is provided with an insulation material between it and the core. A rotary electrical machine such as an electrical motor or generator or the like has a core in which a plurality of teeth are arranged. The coil conductor is placed in the space (slots) between these teeth. In order to ensure insulation between the coil conductor and the core, a sheet of insulating material called a slot liner is placed between the coil conductor and the core.

For rotary electrical machines used in high temperature environments, adequate heat resistance is required for the insulation material. The use of mica for this insulation material is known in the prior art. For the mica used for insulation material, they can be fine flakes of mica or thin pieces peeled from a mica stone. Flaked mica which is hardened with resin is called aggregate mica, and mica in which several leaves of mica peeled from mica stone are held together is called peeled mica.

With the insulation material using aggregate mica as described above, the heat resistance of the resin that binds the small pieces of mica may not be adequate. In addition, because the material is brittle, there may be holes created during manufacturing or there may be holes created by the vibration and the like from the use of rotary electrical machines, and this may result in insulation damage. On the other hand, insulation material that uses peeled mica is not flexible, and it may break when placing inside the slots, and this may result in insulation damage. In addition, peeled mica insulation material is expensive.

In addition, sheet insulation material using mica is not pliant. In particular, when forming the part of the coil that protrudes out from the core end part, what is called the coil end portion, the insulation material bears a load and can easily break. When breaking is a problem, in the prior art, a slot liner was constructed by layering the insulation material using mica with a sheet of the approximately the same size using material with a relatively strong mechanical strength such as resin and the like.

The layer of reinforcement resin of the slot liner described above is interposed between the coil and the core. Under high temperatures, because of expansion or deformation of the resin, the reinforcement layer can separate from the core, and this can prevent the transfer of heat generated from the coil to the core, and the heat radiation capability of the coil is reduced.

OBJECT AND SUMMARY OF THE INVENTION

The present invention considers the above problems. The object of the present invention is to improve heat resistance and strength of the insulation material for the coil of an electrical machine. In addition, the object of the present invention is to ensure the strength of the slot liner of the rotary electrical machine and to prevent insulation damage, as well as to improve heat radiation of the coil.

In order to solve the above problems, the insulation material of the present invention, which is placed between a core and a coil of an electrical machine, is formed by layering at least one sheet each of a peeled mica insulation sheet which has peeled mica as the base material and an aggregate mica insulation sheet which has aggregate mica as the base material. The insulation sheets of peeled mica and aggregate mica compensate for the others disadvantages, and the insulation performance is improved.

In addition, in another mode of the present invention, a slot liner is placed inside slots of a core of a rotary electrical machine and forms an insulation between a coil conductor placed in the slots and the core. This slot liner is formed by layering at least one sheet each of a peeled mica insulation sheet which has peeled mica as the base material and an aggregate mica insulation sheet which has aggregate mica as the base material.

In addition, one sheet of peeled mica insulation sheet can also be interposed between two aggregate mica insulation sheets.

In addition, with the slot liner of the rotary electrical machine of another mode of the present invention, mutually separated reinforcement sheets are placed separately at either end of the slot liner. In other words, the reinforcement sheet is placed near the ends of the main insulation sheet which is placed in the slot and extends in the axial direction of the rotary electrical machine and forms an insulation between the coil and the core. By having the reinforcement sheet receive a portion of the load that is on the main insulation sheet from the coil during the processing of coil ends and the like, the insulation is maintained. In addition, the reinforcement sheet is not present in any other area except for at the ends of the slot liner. As a result, inhibition of heat transfer from the coil to the core due to peeling of the reinforcement sheet is avoided.

For the reinforcement sheet, it is necessary to consider the usage environment of the rotary electrical machine, particularly the temperature. When using resin material, its insulation ability is reduced when there is carbonization resulting from high temperatures. Therefore, it is necessary to select material that is suited to the temperature conditions.

The above, and other objects, features, and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the construction of a stator of an electric motor as one example of an electrical machine.

FIG. 2 shows the arrangement of a slot liner inside a slot.

FIG. 3 shows the cross-section construction of one example of an insulation sheet which constructs the slot liner.

FIG. 4 shows the cross-section construction of one example of an insulation sheet which constructs the slot liner.

FIG. 5 is a schematic cross-section diagram which includes the shaft of the stator core.

FIG. 6 is a perspective view showing another example of a reinforcement sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the figures, the embodiments of the present invention are described below. Referring to FIG. 1, there is a cross-section of a stator of a rotary electrical machine such as a generator or an electric motor or the like. A core 10 of the stator has a roughly cylindrical shape. Its inner perimeter, in other words the surface that faces the rotor, has teeth 12 which are arranged at a specified spacing in the circumferential direction. A slot 14 is the space between teeth 12. Conductors 16, which form the coil, are arranged so that they are stored inside slots 14.

Referring to FIG. 2, there is an enlarged drawing of a single slot 14. In between wire 16 of the coil and core 10, a slot liner 18 as the insulation material is placed along the inner perimeter of the slot. Slot liner 18 is constructed from three layers. Starting from the innermost layer, they will be referred to as an inner layer 20, a middle layer 22, and an outer layer 24. Inner layer 20 and outer layer 24 are of an aggregate mica insulation sheet with a base material of aggregate mica. Middle layer 22 is of a peeled mica insulation sheet with a base material of peeled mica. In FIG. 2, in order to show the construction of slot liner 18 clearly, the thickness of slot liner 18 is exaggerated more than its actual dimensions. A wedge 25 is placed in the opening of slot 14.

Referring to FIG. 3, the aggregate mica insulation sheet is formed by layering a base material sheet 26, which has flaked mica bound and hardened with a resin, and a glass cloth sheet 28, which is woven from glass fibers. In addition, referring to FIG. 4, the insulation sheet can be formed by interposing base material sheet 26, which contains the aggregate mica, between two glass cloth sheets. Middle layer 22, which is interposed between inner layer 20 and outer layer 24, is of a peeled mica base material insulation sheet which has peeled mica as the base material. The peeled mica insulation sheet can also have a two or three layer construction with a base material sheet which contains peeled mica and a glass cloth sheet as shown in FIGS. 3 and 4.

The aggregate mica insulation sheet is flexible and is easy to work with. However, the voltage resistance value is relatively low. The peeled mica insulation sheet has a high voltage resistance value, but easily breaks when bent. In addition, in terms of cost, peeled mica insulation sheets are more expensive. In the present embodiment, the peeled mica insulation sheet is interposed between two aggregate mica insulation sheets. By having this three layer construction, the handling ability when this is inserted inside the slot as a slot liner is improved. In other words, by having the brittle peeled mica insulation sheet interposed between aggregated mica insulation sheets which have a relatively high mechanical strength, the aggregate mica insulation sheets support the peeled mica insulation sheet, and this prevents the concentration of stress and prevents breakage when bending these insulation sheets. In addition, by using two aggregated mica insulation sheets instead of using three peeled mica insulation sheets, the cost is lowered.

In this way, an insulation material and slot liner having the favorable qualities of both the peeled mica insulation sheet and the aggregate mica insulation can be constructed. In addition, varnish can impregnate the aggregate mica insulation sheet well. From this standpoint as well, the insulation capability is improved.

Referring to FIG. 5, there is a cross-section of the stator of the electrical machine as seen from an orthogonal direction to the axis. Slot liner 18 extends in the axial direction of the electric motor, and its length is longer than core 10. Both ends protrude from core end surfaces 30. Slot liner 18 includes a main insulation sheet 32 of the three layer mica insulation sheet, which extends over the entire length, and a reinforcement sheet 34, which is placed only at the two ends. As shown in the figure, a single reinforcement sheet 34 is placed on the outside of main insulation sheet 32 at the position of core end surfaces 30 and also to the positions right and left of core end surfaces 30. In other words, reinforcement sheet 34 is interposed between main insulation sheet 32 and core 10.

Coil ends 38 are part of coil 36, which is housed in the core, and protrude from the core end surfaces. They are molded so that they bend outwards in the radial direction of the rotary electrical machine as shown in the figure. When molding, the portion of slot liner 18 that protrudes from core end surface 30 is pushed, and a bending load is generated. In particular, a large stress is generated at the corner portion of core end surface 30. By having reinforcement sheet 34 disperses this stress, and the stress generated on main insulation sheet 32 is lowered. As a result, damage to the insulation sheet, which is made from mechanically weak mica, is prevented, and insulation is maintained.

Reinforcement sheet 34 is of a polyimide resin. The heat resistance of polyimide resin is extremely high. For example, Kapton (registered trademark) of DuPont has a heat resistance of around 400 degrees C. Because it has such a high heat resistance, reinforcement sheet 34 does not carbonize at high temperatures, and the insulation can be maintained.

Referring to FIG. 5, reinforcement sheet 34 is not present in any other part of slot liner 18 except at the ends. Therefore, the heat generated by the current flow through the coil wire is transferred to core 10 without going through reinforcement sheet 34. In other words, at the center portion of the core, reinforcement sheet 34 does not inhibit heat transfer, and a high heat radiation property is achieved. In addition, although polyimide resin does not carbonize at 400 degrees C., there is shrinkage at temperatures higher than this. When the adhesion between the core and the reinforcement sheet is reduced because of this shrinkage, there is the problem of inhibition of heat transfer. Because of this, reinforcement sheet 34 is placed only at the ends of slot liner 18. In other words, even if there is shrinkage of the reinforcement sheet, because it is only at the ends, the heat transfer at the center portion is not inhibited, and heat radiation is maintained.

Referring to FIG. 6, there is another construction of the end portions of the slot liner. Main insulation sheet 40 has the same construction as the previously described main insulation sheet 28. Reinforcement sheet 42 is placed at the end portions of main insulation sheet 40, in other words at the area near the core end surfaces. Reinforcement sheet 42 is folded. The fold crease is along the end of main insulation sheet 40, and as a result, reinforcement sheet 42 is placed so that it covers the end of main insulation sheet 40. With this, the end portion of main insulation sheet 40 is reinforced even more.

The slot liner of the present embodiment is particularly suited for high temperature environments, for example, in a stator of an electric motor of a canned motor pump which handles high temperature fluids, but it can also be used in other electrical machines with coils. In addition, in the present embodiment, we described having a construction of a slot liner of layering two types of mica insulation sheets and in addition a construction of placing a reinforcement sheet only near either end of the slot liner. However, it is possible to have a construction that uses only one of these. In other words, the construction of the slot liner of layering two types of mica insulation sheets and the construction of placing the reinforcement sheet only near both ends of the slot liner can be used separately.

Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims. 

1. Insulation material comprising: at least one first sheet comprising peeled mica formed of thin pieces peeled from a mica stone and at least one second sheet comprising aggregate mica in contact with said at least one first sheet.
 2. Insulation material as described in claim 1, wherein said at least one first sheet is interposed between two of said at least one second sheet.
 3. An electric device comprising: a core; a coil; and an insulation material comprising: at least one first sheet comprising peeled mica formed of thin pieces peeled from a mica stone and at least one second sheet comprising aggregate mica in contact with said at least one first sheet.
 4. A rotary electric device comprising: a core having a slot; a conductor coil in said slot; and an insulation material between said core and said conductor coil, said insulation material comprising: at least one first sheet comprising peeled mica formed of thin pieces peeled from a mica stone and at least one second sheet comprising aggregate mica in contact with said at least one first sheet.
 5. A rotary electric device as described in claim 4, wherein said at least one first sheet is interposed between two of said at least one second sheet.
 6. A rotary electric device comprising: a core having a slot and end surfaces; a conductor coil in said slot; and an insulation material comprising: a main insulation sheet extending in an axial direction of said rotary electric device, said main insulation sheet having a length equal to or greater than a length of said core; and a reinforcement sheet at each end of said core, said reinforcement sheet on top of an end portion of said main insulation sheet near the end surfaces of said core, a portion of said reinforcement sheet is between said core and said main insulation sheet and capable of reinforcing against a load that is applied to said main insulation sheet.
 7. A rotary electric device as described in claim 6, wherein said reinforcement sheet comprises a polyimide.
 8. A rotary electric device as described in claim 6, wherein said reinforcement sheet has a heat resistance of 400° C. or greater.
 9. A rotary electric device as described in claim 6, wherein: said reinforcement sheet is folded along a crease, wherein said fold crease corresponds to said end portion of said main insulation sheet and covers said end portion.
 10. A rotary electric device as described in claim 6, wherein said main insulation sheet comprises: at least one first sheet comprising peeled mica and at least one second sheet comprising aggregate mica in contact with said at least one first sheet.
 11. A rotary electric device as described in claim 10, wherein said at least one first sheet is interposed between two of said at least one second sheet.
 12. The rotary electric device of claim 6, wherein said coil has a length greater than the length of said main insulation sheet said a length of said reinforcement sheet.
 13. An insulation liner comprising: an inner layer comprising aggregate mica; an outer layer comprising aggregate mica; and a middle layer disposed between said inner layer and said outer layer, comprising peeled mica formed of thin pieces peeled from a mica stone. 